Observations on saliva osmolality during progressive dehydration and partial rehydration



Publication Details

Taylor, N. A. S., van den Heuvel, A. M. J., Kerry, P., McGhee, S., Peoples, G. E., Brown, M. A. & Patterson, M. J. 2012, 'Observations on saliva osmolality during progressive dehydration and partial rehydration', European Journal of Applied Physiology, vol. 112, no. 9, pp. 3227-3237.


A need exists to identify dehydrated individuals under stressful settings beyond the laboratory. A predictive index based on changes in saliva osmolality has been proposed, and its eYcacy and sensitivity was appraised across mass (water) losses from 1 to 7%. Twelve euhydrated males [serum osmolality: 286.1 mOsm kg¡1 H2O (SD 4.3)] completed three exercise- and heat-induced dehydration trials (35.6°C, 56% relative humidity): 7% dehydration (6.15 h), 3% dehydration (with 60% Xuid replacement: 2.37 h), repeat 7% dehydration (5.27 h). Expectorated saliva osmolality, measured at baseline and at each 1% mass change, was used to predict instantaneous hydration state relative to mass losses of 3 and 6%. Saliva osmolality increased linearly with dehydration, although its basal osmolality and its rate of change varied among and within subjects across trials. Receiver operating characteristic curves indicated a good predictive power for saliva osmolality when used with two, single-threshold cutoVs to diVerentiate between hydrated and dehydrated individuals (area under curve: 3% cutoV = 0.868, 6% cutoV = 0.831). However, when analysed using a double-threshold detection technique (3 and 6%), as might be used in a Weld-based monitor, <50% of the osmolality data could correctly identify individuals who exceeded 3% dehydration. Indeed, within the 3–6% dehydration range, its sensitivity was 64%, while beyond 6% dehydration, this fell to 42%. Therefore, while expectorated saliva osmolality tracked mass losses within individuals, its large intra- and interindividual variability limited its predictive power and sensitivity, rendering its utility questionable within a universal dehydration monitor

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